FIG. 7 shows a sectional view of a conventional lens unit disclosed in Japanese Patent Laid-Open Publication No. 04-166905. Cylindrical lens holder 1 includes projections 3 having arc sections on its inner wall. Projections 3 extend along the inner wall and are situated at places which divide the inner wall into quarters. The center of a circle inscribed on the respective tops 3A of projections 3 agrees with optical axis 5 of lens 2, and lens 2 agrees with the inscribed circle. Lens 2 is inserted into lens holder 1, and adhesive 4 has lens holder 1 rigidly hold lens 2.
This lens unit encounters with difficulty of preventing light reflection on the surface of the lens 2 or the surface of lens holder 1. Insertion of lens 2 into lens holder 1 needs clearance 6. Optical axis 5 can be adjusted at accuracy as rough as several tens of micrometers.
FIG. 8A shows a perspective view of another conventional lens unit disclosed in Japanese Patent Laid-Open Publication No. 05-113529. FIG. 8B shows a sectional view of the lens unit shown in FIG. 8A. Outer circumference 12 of lens 11 slants by angle θa with respect to optical axis 15. Inner wall 14 of lens holder 13 also slants by angle θa with respect to optical axis 15. Outer circumference 12 fits to inner wall 14 of lens holder 13, so that lens 11 tightly and solidly contacts inner wall 14 and is held by holder 13.
This lens unit also encounters with difficulty of preventing light reflection on the surface of lens 11 and the surface of lens holder 13. Outer circumference 12 of lens 11 and inner wall 14 of holder 13 slant, hence being manufactured difficultly.